KB5057653: Hotfix update for Exchange Server 2016 CU23, May 2025. Journal delivery, calendar printing and mailbox quarantine issues fixed

This hotfix addresses four Exchange issues, including journal messages stuck in submission and mailboxes quarantined after a background process stops responding. It is for organizations enrolled in the Extended Security Update program.

Does it affect you? Applies to: Exchange Server 2016 CU23 systems in organizations enrolled in the Extended Security Update program. The update package is x64.

Review notes Additional details from the official release notes (1) Read note

What changes HU16 introduces new features and includes all updates from the November 2024 Exchange Server security updates.

The official sources are linked at the end of the page.

For servers running Cumulative Update 23: each cumulative update gets its own update. Support for this version ended on October 14, 2025: Microsoft releases this update only to organizations enrolled in the Extended Security Update (ESU) program, not through Microsoft Update. The others should move to Exchange Server Subscription Edition. Which version am I on?

What changes

Fixes 4 changes

Journal messages

Journal messages that fail during content conversion can get stuck in the submission queue; this hotfix fixes the issue.¹
The affected message returns ConversionFailedException during content conversion.

Outlook on the web

For: Exchange administrators and Outlook on the web users

The listed calendar-printing issue covers Exchange Server 2019 CU14 after its March 2024 security update: selecting Print produces no print job. This hotfix includes a fix for the issue.²
The issue article describes the failure when printing a calendar from OWA after installing the Exchange Server 2019 CU14 March 2024 security update.

Edge Transport service

The Edge Transport service can stop responding and restart while handling certain externally protected messages; this hotfix fixes the issue.³
The failure occurs when Exchange tries to decrypt externally sourced messages protected by Azure Rights Management, including when Journal Report Decryption is enabled.

StoreWorker

A background Exchange process can stop responding and cause affected mailboxes to be quarantined; this hotfix fixes the issue.⁴
The issue is a StoreWorker failure involving BaseViewOperatorDefinition in Exchange Server 2019 or 2016.

Technical details

Data sheet · Security · Downloads · Components Click to collapse or expand

Data sheet

Released: 2025-05-29
Classification: Updates
Type: Cumulative update
Servicing branch: CU23
Replaces: KB5050674, KB5037224
Replaced by: KB5063223

Version	Build	Channel
2016	15.1.2507.57	General availability

Security

No vulnerabilities are listed for this update.

Sources

Updated Oct 27, 2026

Cited passages from Microsoft's official notes (4)

1. For Exchange Server 2016, install: Hotfix update for Exchange Server 2016 CU23 HU16: May 29, 2025 (KB5057653) support.microsoft.com
2. Calendar print doesn't work in OWA from Exchange 2019 CU14 onwards support.microsoft.com
3. For Exchange Server 2016, install: Hotfix update for Exchange Server 2016 CU23 HU16: May 29, 2025 (KB5057653) support.microsoft.com
4. For Exchange Server 2016, install: Hotfix update for Exchange Server 2016 CU23 HU16: May 29, 2025 (KB5057653) support.microsoft.com

Checked automatically: 8 of 8 checks passed, 4 quoted passages · compared with Microsoft's page on Oct 20, 2026

Quotes found in the official pages: passed
Numbers found in the sources: passed
Vulnerabilities from the dossier only: passed
Links to allowed domains only: passed
Every official change covered: passed
Readable plain text: passed
Changes confirmed by the file list: passed
Sources agree: passed

A second AI read the text against the sources: correctness 5/5, clarity 4/5, completeness 3/5. How we work

Published by The Update Bureau. Written with AI from Microsoft's own documents, checked by rules and a second AI. How we work · Report a mistake